The present invention relates to a syringe, especially for dental materials, comprising a cylinder in which a plunger is guided, whereby the plunger is insertable into the cylinder at an end opposite the dispensing socket of the cylinder.
Such a syringe has already been suggested in U.S. Pat. No. 5,938,439. Such a syringe is especially suitable for dispensing dental materials. Such dental materials may have a relatively great viscosity but may also be rather liquid whereby the manipulation temperature plays an important role.
In order to prevent air inclusion upon pushing the plunger into the cylinder through its open end, which air could be dispensed and reduce the quality of the dental material to a considerable extent, it has been suggested in the past to provide the plunger with a longitudinal bore through which the air could escape. In order to prevent that liquid dental materials could also escape through this longitudinal bore, the dental material is briefly polymerized at the side facing the plunger so that its viscosity is so great that it cannot escape through the longitudinal bore.
This method has been successful especially for light and heat curable dental materials whereby, however, the additional method step of polymerization is required which thus delays the filling process.
Various other methods have been suggested in order to allow for a bubble-free placing of the plunger into the piston while maintaining proper sealing of the syringe and to ensure also safe actuation of the syringe. When a gap is provided around the edge, this can cause canting of the plunger especially when it is relatively short with respect to its diameter. Also, the push rod which is used for actuating the plunger, can easily be soiled by the dental material or may get caught in the cylinder.
It is therefore an object of the present invention to provide a syringe of the aforementioned kind, which while maintaining operational safety, prevents reliably the presence of air inclusions when placing the plunger into the cylinder, whereby, however, the manufacturing costs should be reduced also.